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Using the EL7563 Demo Board
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Brief
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May 5, 2003
Introduction
voltages is set to 1.8V. This document outlines the design
consideration and lists the bill of materials and the layout
(Gerber files are available upon request). Please also refer
to the advanced data sheet of EL7563 for detailed
applications of the features.
The EL7563 is a full featured Buck
(Step Down) DC:DC controller with
integrated synchronous MOSFETs.
With very few external components, a 4A step-down DC:DC
converter can be very easily built, resulting in saved board
space, minimal design effort, and improved design time.
If a low current 5V is available, the voltage doubler circuitry
(D2, D3, D4, C9) can be eliminated, resulting in Figures 3
and 4. The 5V VDRV current is typically 2.5mA, 5mA worst
case.
This demo board is operated at about 350kHz switching
frequency. The input voltages are 3V-3.6V and output
C5
0.1µF
C4
390pF
R4
PSHR
C2
C3
22Ω
0.22µF
C1a
330µF
2.2nF
1 VREF
EN 20
2 SGND
FB 19
3 COSC
PG 18
4 VDD
5 VTJ
VHI 16
6 PGND
LX 15
7 PGND
LX 14
8 VIN
VIN
(3.3V)
EN
PG
D2
D4
VDRV 17
C1b
0.1µF
TB408
PGND 13
STP
9 STP
PGND 12
STN
10 STN
PGND 11
C8
D3
C6
D1
0.22µF
0.22µF
C9
0.1µF
L1
4.7µH
VOUT
C7
330µF
R2
820Ω
C10
(NOTE)
2.2nF
R1
1kΩ
EL7563CM
NOTE: Recommended for VOUT ≥ 2.5V
FIGURE 1. EL7563CM DEMO BOARD CIRCUIT SCHEMATIC (VIN = 3.3V)
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Technical Brief 408
\
C5
1 VREF
EN 28
2 SGND
FB 27
3 COSC
PG 26
0.1µF
C4
22Ω
C3
0.22µF
C2
C1b
0.1µF
D3
VHI 24
5 VTJ
C1a
330µF
D4
VDRV 25
4 VS
2.2nF
VIN
3.3V
D2
390pF
R4
6 PGND
LX 23
C6
0.22µF
7 PGND
LX 22
L1
8 PGND
LX 21
4.7µH
9 PGND
LX 20
10 VIN
LX 19
11 VIN
LX 18
12 NC
NC 17
13 STP
PGND 16
14 STN
PGND 15
D1
C8
0.22µF
C9
0.1µF
C10
2.2nF
C7
330µF
VOUT
1.8V
4A
R2
820Ω
R1
1kΩ
EL7563CRE
FIGURE 2. EL7563CRE DEMO BOARD CIRCUIT SCHEMATIC
C5
0.1µF
C4
390pF
R4
PSHR
C2
C3
22Ω
0.22µF
2.2nF
C1a
C1b
330µF
0.1µF
1 VREF
EN 20
2 SGND
FB 19
3 COSC
PG 18
4 VDD
VDRV 17
5 VTJ
VHI 16
6 PGND
LX 15
7 PGND
LX 14
8 VIN
PGND 13
STP
9 STP
PGND 12
STN
10 STN
PGND 11
VIN
(3.3V)
EN
PG
C8
0.22µF
C6
D1
0.22µF
L1
4.7µH
VOUT
C7
330µF
EL7563CM
NOTE: Recommended for VOUT ≥ 2.5V
FIGURE 3. EL7563CM CIRCUIT SCHEMATIC WITH A SEPARATE VDRV
2
VDRV
(4.5V - 6.5V)
R2
820Ω
R1
1kΩ
C10
(NOTE)
2.2nF
Technical Brief 408
C5
1 VREF
EN 28
2 SGND
FB 27
3 COSC
PG 26
0.1µF
C4
390pF
R4
22Ω
4 VS
C3
0.22µF
VDRV 25
C2
5 VTJ
VHI 24
2.2nF
VIN
3.3V
C1a
330µF
C1b
0.1µF
C8
0.22µF
D1
6 PGND
LX 23
C6
0.22µF
7 PGND
LX 22
L1
8 PGND
LX 21
4.7µH
9 PGND
LX 20
10 VIN
LX 19
11 VIN
LX 18
12 NC
NC 17
13 STP
PGND 16
14 STN
PGND 15
C10
2.2nF
C7
330µF
VDRV
(4.5V - 6.5V)
VOUT
1.8V
4A
R2
820Ω
R1
1kΩ
EL7563CRE
FIGURE 4. EL7563CRE CIRCUIT SCHEMATIC WITH A SEPARATE VDRV
EL7563 Demo Board Bill of Material
VIN = 3.3V, VOUT = 1.8V
COMPONENT
LABEL
VALUE
MANUFACTURER
MANUFACTURER’S
PHONE NUMBER
PART NUMBER
Capacitor
C1a
330µF
Sprague
207-324-4140
293D337X96R3
Capacitor
C1b
0.1µF
Any
Capacitor
C2, C10 (Note)
2.2nF
Any
Capacitor
C3, C6, C8
0.22µF
Any
Capacitor
C4
390pF
Any
Capacitor
C5
0.1µF
Any
Capacitor
C7
330µF
Sprague
207-324-4140
293D337X96R3
Capacitor
C9
0.1µF
Any
Diode
D1
Telefunken
1-800-554-5565
BAT42W
Diode
D2, D3, D4
Telefunken
1-800-554-5565
BAT54S
Inductor
L1
Coilcraft
847-639-6400
DO3316P-472
Dale
605-665-9301
IDC-5020 4.7µF
4.7µH
Resistor
R1
1kΩ, 1%
Any
Resistor
R2
820Ω, 1%
Any
Resistor
R4
22.1Ω
Any
NOTE: Recommended for VOUT ≥ 2.5V.
3
Technical Brief 408
Design Considerations
Choosing the Component Values
The following requirements are specified for a DC:DC
converter:
Input voltage range: VIN = 3V-3.6V
4. Output capacitor C7.
∆VO and ∆IL normally decide C7 value. ∆VO requires
ESR of C7 be less than:
∆V O
ESR = --------------------- = 94mΩ
∆I LMAX
Double-check the RMS current requirement of the
output capacitor:
Output voltage: VO = 1.8V
Max output voltage ripple: ∆VO = 50mV
Output max current: IO = 4A
The following steps briefly outline the steps to choose
components. For a detailed design discussion, please refer
to Elantec Application #18 “Designing a High Efficiency
DC:DC Converter with the EL75XX.”
1. Choose the feedback resistor divider.
The output voltage is decided by:
∆I LMAX
∆I C7 = -------------------12
which is 0.15A. For a capacitor or combination of
capacitors with 94mΩ parallel ESR, it is more than
enough to handle this current.
5. Input capacitor C1a.
If all the AC current is handled by the input capacitor
C1a, its RMS current is calculated as:
I INRMS =
R 

V O = 0.992 ×  1 + ------2-
R 1

( D × ( 1 – D ) ) × IO
This gives 2A when D = DMIN. Therefore a cap with 2A
current handling capability should be chosen. However,
in case some other capacitor is sharing current with it,
C1a’s current requirement can be reduced.
Layout Considerations
If R1 is chosen to be 1kΩ, then:
R 2 = 814Ω
Choose R2 = 820Ω
2. Choose the converter switching frequency FS.
The layout is very important for the converter to function
properly. Power Ground ( ) and Signal Ground ( ) should
be separated to ensure that the high pulse current in the
Power Ground never interferes with the sensitive signals
connected to Signal Ground. They should only be connected
at one point (normally at the negative side of either the input
or output capacitor.)
FS, inductor L1, output capacitor C7, and EL7563’s
switching loss are closely related. Many iterations (or
thermal measurements) may be required before a final
value can be decided.
The trace connected to FB pin is the most sensitive trace. It
needs to be as short as possible and in a “quiet” place,
preferably between PGND or SGND traces.
Please refer the FS vs COSC curve to find C4. For
350kHz FS, a 390pF should be chosen.
In addition, the bypass capacitor C3 should be as close to
pins 2 and 4 as possible.
3. Inductor L1.
The EL7563 is internally ramp-compensated. For
optimal operation, the inductor current ripple should be
less than 0.8A.
If ∆IL = 0.8A, then:
The heat of the chip is mainly dissipated through the PGND
pins. Maximizing the copper area around these pins is
preferable. In addition, a solid ground plane is always helpful
for the EMI performance.
Performance
( I – D ) × VO
L = ------------------------------- = 3.2µH
∆I L × F S
The performance curves and waveforms of this demo board
are shown on the following pages, when the junction
temperature of EL7563 is determined by:
where:
1.2 – VTJ
T J = 75 + ------------------------0.00384
VO
D = --------V IN
Choosing L1 = 4.7µH yields ∆ILMAX = 0.53 and ∆ILMIN =
0.43A. L1 should also be able to handle DC current of
4A and peak current of 4.4A at temperature range.
4
Technical Brief 408
Typical Performance Curves
VIN=3.3V
100
96
94
VO=1.8V
EFFICIENCY (%)
EFFICIENCY (%)
VIN=3V
VO=2.5V
95
90
85
VO=1.2V
80
75
70
0.5
1
1.5
2
2.5
VIN=3.3V
92
90
VIN=3.6V
88
86
VO=1V
0
VO=2.5V
3
3.5
84
4
0
0.5
FIGURE 5. EL7563CM EFFICIENCY vs IO
VIN=3.3V
2.505
VO=1.8V
VO=1.2V
1.2
1
0.8
VO=1V
0.6
0.4
VO=2.5V
3.5
4
VIN=3.6V
2.495
VIN=3.3V
2.49
2.485
VIN=3V
2.48
2.475
0
0.5
1
1.5
2
2.5
3
3.5
2.465
0.5
4
OUTPUT CURRENT IO (A)
1.5
2
2.5
3
3.5
4
FIGURE 8. EL7563CM LOAD REGULATION
1.27
1000
900
1.268
800
1.266
FS (kHz)
700
1.264
1.262
600
500
400
1.26
300
1.258
1.256
-50
1
LOAD CURRENT IO (A)
FIGURE 7. EL7563CM CONVERTER POWER LOSS vs IO
VREF (V)
3
2.47
0.2
0
2.5
VO=2.5V
2.5
OUTPUT VOLTAGE (V)
POWER LOSS (W)
1.4
2
1.5
FIGURE 6. EL7563CM EFFICIENCY vs IO
1.8
1.6
1
LOAD CURRENT IO (A)
LOAD CURRENT IO (A)
200
-10
30
70
110
150
JUNCTION TEMPERATURE (°C)
FIGURE 9. VREF vs JUNCTION TEMPERATURE
5
100
100 200 300 400 500 600 700 800 900 1000
COSC (pF)
FIGURE 10. SWITCHING FREQUENCY vs COSC
Technical Brief 408
Typical Performance Curves (Continued)
50
THERMAL RESISTANCE (°C/W)
1.5
VPSHR
1.3
1.1
0.9
0
50
25
75
100
125
46
WITH NO AIRFLOW
42
38
WITH 100 LFPM AIRFLOW
34
30
150
TEST CONDITION:
CHIP IN THE CENTER OF COPPER AREA
1 OZ. COPPER PCB USED
1
2
1.5
3
2.5
3.5
4
PCB COPPER HEAT-SINKING AREA (in2)
JUNCTION TEMPERATURE (°C)
FIGURE 12. EL7563CM θJA vs COPPER AREA
FIGURE 11. VTJ vs JUNCTION TEMPERATURE
95
50
NO AIRFLOW
40
100 LFM
30
20
200 LFM
10
0
EFFICIENCY (%)
JUNCTION TEMPERATURE RISE (°C)
VIN=3.3V
100
60
500 LPF
0
1
2
3
VO=2.5V
90
85
VO=1.8V
80
VO=1.2V
75
70
65
60
0.1
4
0.6
1.1
1.6
IO (A)
FIGURE 13. EL7563CM JUNCTION TEMPERATURE RISE ON
DEMO BOARD
0.6
1.4
3.1
3.6
4
VO=2.5V
0.4
VO=2.5V
1.2
1
0.8
VO=1.2V
0.6
VIN=3.3V
0.2
VO (V) (%)
PLOSS (W)
2.6
FIGURE 14. EL7563CRE EFFICIENCY
1.6
VIN=3.6V
0
-0.2
-0.4
0.4
VIN=3V
-0.6
0.2
0
2.1
IO (A)
0
1
2
3
4
IO (A)
FIGURE 15. EL7563CRE TOTAL CONVERTER POWER LOSS
6
-0.8
0
0.5
1
1.5
2
2.5
3
3.5
IO (A)
FIGURE 16. EL7563CRE LOAD REGULATION
4
Technical Brief 408
Typical Performance Curves (Continued)
50
CONDITION:
EL7563CRE THERMAL PAD SOLDERED TO 2-LAYER
PCB WITH 0.039” THICKNESS AND 1 OZ. COPPER ON
BOTH SIDES
45
40
35
30
40
TJ RISE
θJA (°C/W)
45
35
25
20
15
10
30
5
25
0
1.5
2
2.5
3
3.5
4
0
1
PCB AREA (in2)
FIGURE 17. EL7563CRE THERMAL RESISTANCE vs PCB
AREA - NO AIR FLOW
1.5
2
2.5
3
3.5
FIGURE 18. EL7563CRE JUNCTION TEMPERATURE RISE
ON DEMO BOARD - NO AIR FLOW
Demo Board Waveforms
VIN=3.3V, VO=1.8V, IO=0.2A-4A
VIN=3.3V, VO=1.8V, IO=4A
∆VIN
VLX
IO
iL
∆VO
∆VO
FIGURE 19. SWITCHING WAVEFORMS
FIGURE 20. TRANSIENT RESPONSE
VIN=3.3V, VO=1.8V, IO=2A
VIN=3.3V, VO=1.8V, IO=4A
VIN
VIN
VO
VO
FIGURE 21. POWER-UP
7
4
IO (A)
FIGURE 22. POWER-DOWN
Technical Brief 408
Demo Board Waveforms (Continued)
VIN=3.3V, VO=1.8V AT 4A
VIN=3.3V, VO=1.8V AT 4A
EN
EN
VO
VO
FIGURE 23. ENABLE
FIGURE 24. DISABLE
VIN=3.3V, VO=1.8V, IO=4A TO SHORT
IO
VO
FIGURE 25. SHORT-CIRCUIT PROTECTION
Demo Board Layout (EL7563CM)
1000 mil
2000 mil
FIGURE 26. TOP LAYER
8
Technical Brief 408
Demo Board Layout (EL7563CM) (Continued)
1000 mil
2000 mil
FIGURE 27. TOP SILKSCREEN
1000 mil
2000 mil
FIGURE 28. BOTTOM LAYER
1000 mil
2000 mil
FIGURE 29. BOTTOM SILKSCREEN
9
Technical Brief 408
Demo Board Layout (EL7563CRE)
2 in
2 in
2 in
2 in
FIGURE 30. TOP LAYER
FIGURE 31. TOP SILKSCREEN
2 in
2 in
FIGURE 32. BOTTOM LAYER
2 in
2 in
FIGURE 33. BOTTOM SILKSCREEN
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